First, I want you to see the video linked to below called “Cellgrazing.” It is short and fun to watch. (I recommend opening in a new window or tab so you can come right back to this post). Then I will explain why what you are seeing is important.
Cody Wood opens the electric fence, allowing 160 sheep to move from one acre to another.
Now let’s play a game of “What if?”
What if you brought a 10 year old kid to an all you can eat buffet and said, “Get whatever you want. I am not even going to look at your plate. Here’s $10. Eat up.”
Now, if you were to look at the plate what might you see? A perfectly well balanced diet, or heaps of fried chicken and chocolate éclairs?
What holds true for kids holds true for grazing livestock: It is best not to give them too much choice in what they eat, but instead guide them towards a balanced meal.
Most pastured livestock in the U.S. are managed akin to “free reign at the buffet.” Typically, a 50 acre field is stocked with a few hundred sheep or 50 cattle. They get a month or more on a field then are moved to another (often called “alternate grazing”). In that time the animals learn to seek out their favorite foods and avoid the areas of less tasty forage. A decline in pasture quality can really be quick—happening within a summer. For example, if the pasture originally was rich in clover that may be gone in late summer, with mostly tall fescue remaining. Come back in a few years and the less desired plants dominate the field all year long.
We avoid this problem by doing what is called intense rotational grazing, or cell grazing.
Explaining Cell Grazing
Cell grazing places the entire herd into a small area each day. At Fern Rd Farm, for example, we are giving the animals about 1 acre per day. Currently, all 160 sheep are restricted to these mobile paddocks. This equates to about 15,000 lbs of livestock per acre per day. On very well established, perennial pasture we could probably stock two to three times as intensively.
These 15,000 lbs of livestock will eat about 750 lbs of plant matter each day. Ideally, each paddock starts off with 2-3 times this amount of biomass so that after grazing enough residual biomass remains to rapidly rebuild standing biomass. It is a bit like interest growing in a bank account: residual biomass is like the remaining principal after a withdrawal, and as long as enough remains the account will quickly rebound to the former size. Over graze, however, and not enough principal will be there to rapidly regenerate.
Residual biomass after grazing is shown in the foreground, while the other side of the electric fence is actively grazed.
Forcing animals into a small space may also have a psychological effect on them. They sense the proximity of others and learn that this is all they are going to get for the day. This makes them less picky and more eager eaters—sort of like putting a casserole in front of 8 hungry brothers and saying “Here’s your supper.” The animals eagerly run from one paddock to the next, and (as the video above attests) it is a lot of fun to watch them begin eating with fervor.
This system also improves forage quality. Explaining this can get a bit technical, but I’ll try to make it clear.
Pasture experts talk about the S-curve. This refers to changes in the rate of growth of the stand of plants. When plants are very small, they put on only a small amount of biomass per time. But at a certain size, the amount they add each day increases rapidly. Of course any exponential rate of growth must end, and so growth slows and halts as the plants reach maturity. S-curves are common in all biological growth systems. What good pasture management does is keep animals eating as much of the pasture before it reaches the mature, no growth stage, but not so much that the pasture has a very long recovery time because the plants have been eaten back to the slow-growth portion of the S-curve.
Best management practices keep the pasture stand within stage 2 of the S-curve as much as possible.
It turns out that nutritional quality is best during this rapid growth phase too. Plants growing rapidly are full of readily digested sugars and proteins—you can literally taste this yourself when chewing on a grass blade. This makes sense since sugars and proteins are the building blocks of new cells and the growing plant is, by definition, building new cells at a rapid clip.
By contrast, an old plant is very sturdy with rigid cells that are not producing a lot of available sugars and proteins. Nutrients may be going down to the roots for winter storage, or into reproductive parts such as flowers and seeds. Well managed grazing delays the senescence process to yield more productivity as measured by captured sunlight and conversion to biomass each year.
This management system is not only more profitable on a per acre basis each year, but it also improves the soil over time.
Plants pulsing up and down the stage 2 portion of the growth curve are pumping carbon into the soil. Increasing soil organic matter is one of the best ways to add value to the land over time. Fields high in organic matter will buffer the water supply and keep nutrients from washing out during wet spells. I won’t get into the biophysical reasons for this, but it is like adding a layer of sponge to the soil, and when you walk on the fields it may even feel spongy.
Cell grazing is a great example of applied science—the reasons why it works are well understood from basic principles of plant biology and ecology—but getting it right in practice takes a great deal of expertise and skill. My job as farmland manager for Farmland LP is to make sure we put together the farm infrastructure and on-farm skilled practitioners to improve the land while producing healthy food and steady income.